I brought up not wanting someone to be the god of smithing and metalworking, teaching the tribes iron or steel.

One of my players had this idea.

I have an idea: when you're thinking of something like the smithing example, ask a question.

"Has anyone ever done this before?"

If nobody in the setting has ever worked out how to bang that piece of iron into something useful, then the Gods don't know either. After all, Gods are powered by the Belief of those that worship them, and if the worshippers couldn't possibly know how to make something out of iron, then how will the God? They may well have to learn it from other spirits - or steal it, a roleplaying task in and of itself. Hell, we haven't even invented the wheel yet.

In the Neolithic, a God of Smithing wouldn't exist yet, since humanity hasn't quite got the concept down yet. A God of Mining would know about gold, silver and copper (reasonably easy to work with) but iron isn't quite in their purview yet

Your conclusions are good. If the tribe does not know, the god does not know. Now if you want to say your tribe has been around for some time and has a lot of Knowledge then a god of Knowledge would know everything all the tribe has ever known.

Another idea for your god of Knowledge is to gather more ideas from the elder races. He can teach slowly new ideas if gathers them in the first place from other locations. If your god transformed into a slyph and went to the Crater of Lugos to learn, this can be possible, but both players and GM must determine beforehand knowledge and what is possible during the sessions. This has lots of role-play opportunities and can also lead to other scenarios such as war over technologies between tribes and so forth.